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Old 09-03-2002, 07:35 PM   #1
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Measuring Amp draw by a discharger, HELP!

Hey all. How do you measure the Amps being drawn by a discharger? I have heard my indi reactor 20 can draw more than the stated 20 amp discharge rate, I have heard of it drawing up to 27 Amps at times and I want to check this when discharging a pack so I make sure my discharge times are correct.


PS- I have a radio shack volt meter, if I can use this, how do I go about measuring the draw?
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Old 09-03-2002, 09:21 PM   #2
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Connect your multimeter in series with your discharger. Dial the amp reading to a higher range than one you'd expect. Then dial down the reading range in steps such that you can obtain a reading to the closest 0.1 A.
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Old 09-04-2002, 12:29 AM   #3
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Most multimeter that can measure amp will work up to 10A only. You will blow the fuse or may damage your multimeter if you connect 10A meter to 20A. One of the good way to measure high current is clamp meter but it can be expensive.

You might try to connect very low resistance in series with the battery and measure its voltage instead. You can calculate the current by ohm's law V=IR -> I=V/R. For 20 amp I think that you will need .01 ohm or lower resister because the voltage drop in the resister will cause you discharger to misread the voltage (0.01 ohm@10 amps = 0.1 volt). The problem is that .01 ohm resister is hard to find but you can also use 10 of 0.1 ohm resistors connected in parallel.

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Old 09-04-2002, 01:39 AM   #4
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You can't measure current with a voltmeter... you'll need an ammeter for that...

If you have a multimeter, check that the maximum current it can measure is more than the expected measurand (i.e. 20 Amps). If it is less then you'll have to buy an ammeter...
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Old 09-04-2002, 04:41 AM   #5
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Yes, use a small resistance of 0.1 Ohm or under. However, no accurate measurements can be made this way. If you only want to measure if the current draw is stable, just measure the voltage across 10 cm of wire. You'll be surpriced of how much voltage drop normal electrical wire has! After I measured the resistance of the wires of my battery analyzer, I replaced the wires on my race car ;-)
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Old 09-04-2002, 12:36 PM   #6
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The hobby shop owner has a multimeter, i probably will see him saturday to setup my stuff.

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